1. Field of the Invention
This invention relates generally to FM radio receivers. In particular, this invention relates to a front-end for processing a multiplex FM radio signal such that data content in the multiplex signal may be recovered inexpensively and without undue complexity.
2. Related Art
Modern FM radio transmissions include several types of content. In most cases, the FM radio signal for a particular channel is a multiplex signal that includes not only left and right channel audio content, but also data content. The data content typically takes one of two forms; either Radio Data System (RDS) data content (commonly used in North America), or Autofahrer Rundfunk Information (ARI) data content (commonly used in Europe).
Radio stations insert many different types of information into the data content. As examples, the data content may carry program identification codes that indicate the name of the audio program provided in the program content, the name of the radio station broadcasting the FM radio signal, news, advertising, traffic reports, alternative reception frequencies for the audio program, and so on. Processing circuitry in the radio decodes the data content and outputs the corresponding information on a display.
In the past, receiving and processing the data content has met with several disadvantages, summarized below with reference to FIG. 1. In particular, prior radios included a receiver that output the multiplex FM radio signal to a highly specialized analog RDS demodulator. The analog RDS demodulator included circuitry for recovering, from the FM radio signal, digital RDS data that the demodulator provided to a subsequent processing stage using a data output and a clock output.
However, the analog RDS demodulators were complex devices with a relatively high price tag. In part, their expense derived not only from their specialized nature, but also from their tendency to include a great deal of additional processing circuitry for other purposes. Thus, for example, some RDS demodulators also included signal quality estimators, digital communication interfaces, and the like. As a result, FM radios were subject to undue increases in cost and design complexity when they included RDS information features.
Increasing the cost of the radio is, of course, undesirable from many standpoints, including design and manufacturing as well as consumer purchasing. Therefore, there is a need for methods and systems for processing the data content that do not suffer from the shortcomings set forth above, or others previously experienced.